Why does the synchronizer chain "altera_std_synchronizer_nocut" have unsafe MTBF in the metastability report in Timing Analyzer?

Description

Due to a problem with the Quartus® Prime Pro Edition version 19.1, the synchronizer chain "altera_std_synchronizer_nocut" might  have an unsafe Mean Time between Failure (MTBF) when it follows an asynchronous transfer. This is because the synchronizer chain is merged with retimer-created registers, which breaks the synchronizer requirements. Without a synchronizer, an asynchronous transfer will have a very low MTBF and be reported as being unsafe.

Resolution

To work around this problem for the Quartus® Prime Pro Edition Software, turn off the early retimer by writting the following assignment in the Quartus Settings file (.qsf):

"set_global_assignment -name FITTER_EARLY_RETIMING OFF" 

This problem is fixed beginning with version 19.2 of the Quartus® Prime Pro Edition Software version.